<svg width="100%" height="100%" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <pattern id="grid10" width="10" height="10" patternUnits="userSpaceOnUse">
      <path d="M 10 0 L 0 0 0 10" fill="none" stroke="#363637" stroke-width="0.5"></path>
    </pattern>
    <pattern id="grid50" width="50" height="50" patternUnits="userSpaceOnUse">
      <rect width="50" height="50" fill="url(#grid10)"></rect>
      <path d="M 50 0 L 0 0 0 50" fill="none" stroke="#414243" stroke-width="1"></path>
    </pattern>
  </defs>
  <rect width="100%" height="100%" fill="url(#grid50)"></rect>
</svg>